Propeller or rotor construction



March 11, 1941.

R. H. PREwlTT 2,234,196

PROPELLER 0R ROTOR CONSTRUCTION Filed July 51, `1955 2 Shoets-Shot i I?Zw' d@ d.

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r z'caral EPrewf/'Z I March 1K1,` 1941. R HfPREwlTT 2,234,196

l"ROPlILII.J3}R- 0R ROTOR CONSTRUCTION Filed July s1, 193s 2 Smets-shut2- BJgz'C/zard E Previti 'Patented Mar. 11, 1,941

UNITED STATES PATENT OFFICE l 42,234,196 I PROPLLER on. Ro'ronCONSTRUCTION Richard HQPrewtt, Lansdowne, Pa.

Application July 31, 1935, Serial No. 34,023 s claims. (ci. 17o- 164)The present invention relates to certain new -and useful variable pitchpropellers for aircraft either for propelling aircraft in forward ightor for providing vertical lift for aircraft.

The object of the present invention is to so juxtapose the variousforces which can act upon a. propeller blade or rotor blade, and to sodetermine the direction and magnitude of these forces relative to eachother as to effect any desired and predetermined blade angle setting forany operating'condition. 4 ,l

Another object of the present invention isfto provide means whereby thepitch of the propeller or rotor blades will tend to settle pinto anequilibrium position at or near their most effective angles of attack inall conditions of opera-f tions'.

A. propeller or rotor in accordance with my invention comprises aplrrality of blades each mounted on an individual pivot making an acuteangle with the plane perpendicular to the main axis of rotation of thepropeller or rotor. The angle for the blade pivot having once been iixedand other constants of the device settled on 25 which are ordinarilyconsidered in design of a propeller or'a rotor for lifting purposes, the

characteristics of a .given installation can be readily determined sovthat the blades will automatically set themselves on their pivots tohave attack for any given speed of rotation or translation underconstant operating conditions.

A Thus, by setting the pivot axis of the blade so that the line .of thepivot axis will diverge from the plane perpendicular to the axis ofrotation (sometimes more commonly termed the disc)` in a directionopposite to the intended lift of the propeller or rotor, theaccelerating torque incident to power input will tend to increase the 40bladeangle, whereas if the pivot axis is so disposed that the line ofthe pivot axis diverges from the plane perpendicular to the axis ofrotation in the same direction as the intended direction of the lift ofthe propeller or rotor, then the torque incident to power input willtend to decrease the blade angle; the former disposition vof the pivotaxis being preferred for propellers intendedV to supply forwardpropulsion of the craft, or propellers or rotors intended for normaloperation either for vertical lift under power or for auto-rotationalsustention, while the latter disposition of .the pivot. axis is the onepreferred whenever it is desired to increase the R. P. M.'

of a rotoror agpropeller-like structure without l' increasing its thrustor lift and where it is dea favorable, if not indeed the optimum angleofV siredto decrease the induced drag during such power input.Conversely, the cessation of accelerating powerrinput causes a decreasein pitch angle in the first case and an increase in incidence in thesecond case. g Likewise, by predeterminingthe direction and magnitude ofthe aerodynamic forces on the blade in relation to the location of thepitch-V varying blade pivot axis, the relationship between aerodynamicforces the pitch-varying blade pivot axis is so arranged according tothe present invention, as to automatically tend to vary (increase ordecrease) the angle of incidence of the blades (the angle of .the`bladeto the disc) in such a way as to tend 15 to iioat'the blade at apredetermined effective angle of attack (that is, yat a givenpredetermined weighted average angle of 'attack regardless of thechanges in the magnitude and direction of air flow with respect to discor blade ele- 20 ments). Such predetermination of direction andmagnitude of aerodynamic forces in relation freely pivoted butnon-revoluble air foils is disclosed in my Patent No. 1,989,291.

By balancing the torqueforce, the inertia of the blades resistingrotation, the centrifugal force on the`blades, and aerodynamic forces onthe blades, the balanceor equilibrium position is attainable in whichthe blades will have alternately the most eilicient angle of attack forAany one of several operating conditions.

So also by suitably proportioning the several different forcesv and/orthe turning moments through which they act, a variable equilibrium pointis attainable for the variant operating conditions, as for instance, thecondition of starting and 'the condition of full R. P. M., or thestationary condition of the craft, or the full speed' of the craft, orthe condition of full torque, or

free-wheeling.

The centrifugal force acting on the masses tends to retain the 'mass inits outermost posi tion with respect to the axis of rotation l,ofpropeller or rotors, and thereby opposes all other forces which may actupon the blade, tending i5 to displace it from such outermost position.v

In addition to the torque due to power input and the inertia of theblades (which, in combination with the torque, tend to turn the bladesabout their respective pivots), and .in addition to the centrifugalforce Which may tend to op\ pose such turning, the aerodynamic forcesare made to favor or oppose such turning by the use of an air foilsection, and by so locating the pitch-varying blade pivot axis inrelation to the and the location of 10V Y Figure 1 is an elevationalview, 125.

resultant air-load vectors of section, that the moments about thepitch-varying blade pivot axis will cause the blade to tend to float ata given angle of attack (that is, the disc component of the aerodynamicforces will be fore or aft of the blad j With the above and otherobjects in view which will appear more fully from the followingdescription, the present inventioncontemplates a'propeller or rotorhavingeach of its blades pivoted about a. plvotidisposed y at an angleto the longitudinal axis of centrifugal forces,'the aerodynamic forcesandthe torque forces, acting upon the blade, willcreate to influence theblade setting of the blade.

The present invention further consists of other novel features anddetails of construction, all of which will appear more fully from thefollowing detailed description and accompanying drawir-Kings..

In the drawingsz- Y partly' in section and partly diagrammatic incharacter of one embodiment of a propeller in accordance with myvinvention for propelling aircraft inforward night. 'I'he point Bindicates the centerjofair thrust or load for the. entire blade whilethe plane perthe longitudinal blade axis and containing` the line B-,Pis the plane of the resultant air load vectorsl and the point P is thepointl at which the pivotal axis A-P pierces the plane of the` resultantair load vectors, that is, where Ithe pivotal axis 'and the plaine oi.'the` resultant air load vectors intersecteach other. I

Figure 2 is a diagrammatic representation of a section of a blade lforany of the embodiments of the present invention, on a plane passingthrough the longitudinal center of air thrust or load for the entire'blade perpendicularly to the ylongitudinal blade axis; 'said plane beigherein vectors. The vectors shown in Figure 2 are illustrative of theresultant air load vectors on the blade at thevarious angles of attackindicated for purposes of illustration and the sector of` the area ofthis plane bounded by the vectors a and f isthe stable region oftheblade Figure 3 is a detailed plan4 vlewshowing a collar and pins usedin manually al'iiusting` or setting pressure against the blades theangleof the blades in Figurel. X Figure 4 is a detail of the leverforactuating the collar shown in Figures 1 and 3.

i -Figure 5 is' a fragmentary plan `\view of the locking sector and handlever shown in Figure 1 l and forming part of the means for manually ad-Y 1 justing the blade angle. l

Figure 6 is a detail sectional view on the line 1s-cofrigur'e'1. l

Figure 7 is an elevational view of a second form of propeller embodyingmy invention, a part being c/ ut away for purposes of illustration.

Figure 8 is an end-view taken fromthe left of Figure 7. part being cutaway for purposes of` illustration. l v

f Figures 9 and 10 are respectively a side viewand i a.j plan view of apr er type rotor in/ accordance with my invention forv providingvertical lift rigresn and'ia are `respectively a. side aliat 'plan vdewof a second form of .propeller type rotor 'in accordancel withv myinvention.' l Figures- 13 and 14 are respectively-a side view the bladeso that the.

turning moments aboutv such pivot axisv eective angle setting or pitchpendicular to the vline B-B` or perpendicular to' referred to as theplaneo! the resultant alr load and; plan view of a third `form ofpropeller type rotor in accordance with my invention.

The propeller installation illustrated in Figure 1 comprisesa driveshaft i6 whose axis of rotation is represented by the line AC. Fixed onthe shaft- 5' i6 is a sleeve i8 having ahub 20 formed atithe outer endthereof, and on which are gudgeons or pivots, one for each'blade 2d ofthe propeller, one such pivot appearing at 22. As appears clearly in'Figure l, the axis AP of each pivot 22 lies in a i0 plane radial to themain axis of rotation AC and at an angle to the plane perpendicular tothe axis of rotation AC so that each pivot axis intersects the axis ofrotation. LThe longitudinal axis AB ci each individual blade, however,lies also at an x5 angle to the axis of its pivot Y22, each blade root26 having a blade root bracket or'a'rm 2d onset therefrom and.iournalled on the pivot 22. However, it is not essntialthat ,the bladeaxis or f' pivot axis always intersect the axis of rotation. Eachblade-root bearing bracket or arm 28 has a series of segmentallyarranged teeth 3B 'thereonA which mesh with a similar sexies o`f teeth32 on a segmental gearing 34, whose hub has the form of an outer sleevesurrounding the sleeve member i 8; 'Ihe blades 24, therefore, areconnected together through gearing consisting of teeth 30 and 32, sothat they must turn about their axes '22 simultaneously and with equaldegree. However,as will hereinafter appear, it is not necessary to con-3 -nect individualblades in this manner. The sleeve portion of the gear34 has circumferential slots therein, one of which appears at 36, andthe sleeve I8 has pins 38 thereon projecting into slots. 36 so as' tohold the segmented gear 34 in ixed position longitudinally of member I8,and tolirnit the' degree of rotation of the segmented gear 34,`there bylimiting the rotation of the propeller blades about the axes The bladeroots 26 and bladeroot brackets or arms 28 are shown'as formed sepa.- 40rately and clamped together by bolts 40, but I do not limit myself tothis feature of construction.

In thev form of construction shown in Figure 1 as the blades 24 swingabout the axes A-P they change their angle of attack. I prefer toarrange, 45'- the blades 24 of a propeller for forward motion l so thatan eillcient angle of. attack will occur (as for instance 5.4.o shown inFigure A2) when the center of mass of the blade is in its outermost`position-with y AC-that is, farthest from said axis. In the embodimentshown in Figure 1, the disc drag or air parallel to the plane q f thedisc, tends to turn the blades about the axes AP of the pivots 22 andthereby to increase 55 thel angle of attack Auntil an angle of attack isl reached such that the resultant vector -repre- '.senting. the totalair forces passes through the pivot axis AP. As the blades turn aboutthe axes AP, howeverI they move away from the perpendicular to the axisAC, andthe angle between their individual longitudinal axes and theplane perpendicular to the main axis of rotation. AC becomesgreater'andapproaches more nearly that of the axes AP. The turningmoment due to drag, about AP therefore are less effect e-as theircoupler arms, shorten. The blades "thereby become increasingly subject.to a centrifugal force tending to throwl them back toward thel planeperpendicular to AC. Y ,7 A balance is therefore soon produced between,`the centrifugal forces and the air pressure with reference to the axesAP for any constant speed f of rotationv or constant rate ofacceleration. 'This position or point of balance is one in which the 75respect to the main axis of rotation 5. I

storing moment is designed to total turning moment acting on each bladeabout its individual axis AP is zero, and occurs at a different angle orposition of the blades with respect to axes AP for each differentcondition of operation of the propeller. However, there is a particularangle of attack at which the propeller acts most efliciently at eachgiven speed. It is evident, therefore, that the point of balance betweenthe forces on the-blades about their individual pivots and the mostelcient angle of attack for the given constant speed of rotation shouldoccur simultaneously. The solution of the problem of forming themechanism to act in this manner can be readily found by one accustomedto the design of airplane propellers.

When marked changes in the throttle setting i are made, material amountsof kinetic energy. are transferred from 'the propeller shaft to theblades or from the blades to the shaft due to the inertia of the bladesand such inertia effects set up turning moments on the blades about theaxes AP throwing themrearwardly or forwardlyl of the position desired.-However, the movement due to inertia is, in general, in the direction inwhich the air pressure will tend to move the blade as the speed changesdue to the change in throttle. For instance, in the form shown in Figurel, an increase in throttle opening causes an acceleration of thepropeller hub'while the blades lag behind the axes AP, thereby throwingthe blades toa position of higher angle of attack.

Furthermore, if desired for obtaining automatic stability, the propellerblade can be given an airfoil section such as that shown in Figure 2 inwhich, as the angle of attack increases, the resultant air-load vectorrepresenting the total air forces on a given blade moves aft inrelation, to the pivot AP and as the angle of attack decreases thevectors move forward in relation to said pivot. The action of theseresultant airload forces about the pivot AP cause turning moments aboutsaid'pivot, which, either by themselves or in combination with thecentrifugal re.-` storing moments about the same pivot tend to keep theblades floating at a predetermined angle of incidence. For example, ifthe centrifugal rebe substantially zero when the blade isat 55.40 innormal flight, the blade will automatically tend to operate at thisYpredetermined angle of attack. Should the blade be momentarily shiftedinto a higher angle of attack due to accelerating forces or momentarychanges in air-flow, the air load forces would tend to rotate the bladeforward into lower angles of attack. On the other hand, should the bladeangleof attack be altered into lower angles of attack due todecelerating forces or momentary changes in air-flow the air loadvectors representing the lower angles of attack being located forward ofthe pivot AP will tend to rotate the airfoil blade back into higherangles of attack. Such shifting of the total air load vector causes abalance to be reached between al1 the forces involved with a much lessvchange in angle of incidence than would otherwise be the case.

The way in which the angle of attack of the blade, and the correspondingway in which the center of pressure of the blade 24 shifts transverselyof the blade is'indicated in Figure 2 by a series of vector lines, a, b,c, d, e, and f, representing the resultant air loads for the airfoil orblade at several angles of attack. Each of the lines a, b, c, d, e and fintersects chord line I2, of the blade 24 at the centerof air pressure,

the angle of attack for written thereon. v

The section shown in Figure 2 and the resultant aerodynamic forcesindicated therein are the section and forces at the longitudinal loci 5of .centers of pressure and the longitudinal loci of resultantaerodynamic forces. Y

As indicated-diagrammatically in Figure 2, the blade cross-section ineiect swings about the pivot AP and in doing so the presented at varyingangles to a constant air ilow present, thereby varying the angle ofattack as the blade section swings about the pivot AP. Should theair-now change its angle of attack in relation to the blade, as is thecase in changing the velocity relationships between the flow in thepiane ofthe disc and the flow normal to the disc, the resultant air-loadvectors will automatically keep the blade oating at or approximately thepredetermined effective (that 20 is, weighted) angle of attack.

It may be noted that as the blade swings around the pivot AP into higherangles of attack shown on the right of the diagram become operative andtend to rotate the blade forward into lower angles of attack. Should theblade move into iower angles of attack, the vectors on the left of thediagram representing the resultant forces at these lower angles ofattack become operative and tend to rotate the airfoil back into vhigherangles of attack. Thus, it is apparent that, for the air loads acting onthe airfoil,and in the construction shown the blade will stably pivot ata certain angle of attack (5.4") for each given stable operatingcondition.

It'will be understood that the blade 24 has an angle of attack of 5.4when in what I call itsv neutral position, that is, the position inwhich the 40 blade is most nearly at right angles to the axis ofrotation AC. The lines representing the aerodynamic forces moveprogressively toward the trailing edge of the blade, lying to the rearof the axis AP at all angles of attack greater than 45 5.4 andprogressively forward of the pivot APk at angles of attack lower than5.4". Airfoil sections in which the center of pressure moves rearwardlywithincreasing angle of attack are known as stable sections, and thestable area at the 50 plane of the resultant air load vectors showninFigure 2 is designated as a stable region. In myI Patent No. 1,989,291 Ihave' described more fully t'hese stable areas of the resultant air loadvectors and have shown the location of a pivot axis for 55 an air foilin these stable regions and have shown the resultant stability of anglesof attack through changes in air flow within a practical range. Thepresent invention contemplates the application of such relationshipbetween airfoil andvpitch-vary- (50 ing pivot axis in revolving airfoilsboth under freely revolving conditions and under powerdriven conditions.

vA stable region in the plane of the resultant airl load vectors, may bedeiinedas that region in 65 which the resultant air load vectors arearranged in consecutive increasing order of respective angular attack ofthe airfoil from the leading edge direction to trailing edge direction.An air load vector may be defined as a of the effective air forcesacting on an airfoil when operating under one set of conditions. Thecenter of pressure of an airfoil is that point located in itscross-section at which au,` the air forces acting on the blade at anyone time 75 each vector line beingV f blade section is 10.

the vectors representing higher angles of attack 25 line representingall 70 assumed tobe concentrated.

An airioil moving through air and having thel air forces acting upon it(which'air forces may lift it,` move it, or otherwise displace it in anyway) may' be said to have a so-called center of pressure, that is, thepoint at which all the air f'fo'rces* acting on the airi'oil in aparticular air- 'ow orang'le of attack, maybe said to be conf centrated,vso that if a single force of a resultant f magnitude and directionwereapplied to that one ..cation'o the center of pressure has a much morepoint, such single force would have the same ef- 'fect on thedisplacement or tendency to displace the -airfoil as though thedistributed air were-acting on it.

This center of pressure may be considered 4either chordwise orlongitudinally (orA lengthwise) of the airfoil. To locate the center ofpressure definitely; it m`ust therefore be locatedv both chord-wise andlengthwise of the airfeil.y

Where the airfoil travels through the air or where the air idows over orpast the airfoil in a 'chord-wise direction, at -a generally constantangle throughout'the` length fof' the airfoil, then a variation in thelongitudinal angle of the alr- :lfoil will not greatly shift thelongitudinal'disposition r location of the center of pressure. Thiscould perhaps be .easily exemplified yby the wings'- or. a fixed-wingairplane, wherera slight increase or decrease in thedihedral angle ofthewings will not greatly shiftV the centerof air `pressure longitudinally,and whatever shift does-take place longitudinally does notvgreatly'affect ultimate stability.,

Where the .,airfoil. travels through the air chord-wise but with aconstantly changing angle between the` direction of ilow of air andthelongitudinal direction of the airfoil, such as infrotative wingedaircraft, then -the center of pressure does tend to shift alsolongitudinally, re-4 sponsive to the changes in angle between the airo'w,and the longitudinal direction of the 'airfoiL For vthe purpose ofairfoils, the treatment and consideration of the chord-wise location ofthe center of pressure has been unlversallyconsldered the more criticalstudy, because of the. fact thatthe chord-wise location or variationin,lo

profound influence on the functions and utilityv and efficacy ofthe.airfoil. Even in the consideration andanalysis of airfoils ofrotative sustention systems, or, more broadly, rotative thrust producingsystems, the chord-wiselocation of the center of pressure is of primaryconsideration, whereas the longitudinal location of the' center ofpressure is of secondary consideration from the standpoint of theaerodynamic functions, utility and emcacy of the bladev (not, however,from the standpoint of resonance, bendingmoment and some ofthe' otherconsiderations which enter into theactual mechanical operation of therotative sustention or thrust producing system).

` With 'respect to the chord-wise location` of the called'fixed` centerof pressure In /the fixed-center-of-pressure airfoils, the

center lof pressure of an airfoil, airfoils'have intotwha't may be beenclassified, inter alia, l

airfoils andl migratory center of pressure airfoils.

center of pressure (chord-wise) remains lxed v 2,234,196 4or under anyone set of airc'miitionsv may be over vthe practical range of operation,notwithstanding the changes inthe angles of attack. In ,the other classof airfoils. which may here be called migratory-center-of-pressureairfoils; the center oi' pressure shifts chord-wise with changes inangles of attack and responsive to such 5 changes in angle of. attack.These two clses of airfils have been well-known and recod and variouslyused in the past, as 'for instance the use ofAmigratory-center-of-pressure airfoils of the stable type. in my earlierPatentv No. 1,989,291.

`,The migratory-center-of-pressure airfoils in turn have been of twokinds; broacily, those, on one hand, in which the center-of-pressuremigrated rearward with decreases in angle' of attack and migratedforward with increases in angle of attack (within practical range ofintended operation) and those, on the other hand, in which thecenter-of-pressure migrated forward with decreases in angle of'attackand migrated rearward with increases ini-angle of attack. 'I'he latterhave been generallyregarded. as stable airfoils and the former generallycalled "unstable a'irfoils. l 'f The reason why the latter kind ormigratorycenter-of-pressure airfoil isgenerally regarded as astableairfoil in the aeronautic world, is that the airfoil is inherentlyself-compensating against finstability, namely, itautomat-icallycounteracts I attack. Thus, for instance, an increase of angle of attackwillv move the center-of-pressure rear- .wardly inrelation to the centerof gravity and thereby enable this change in relative location of f 'thecenter of gravity to tend to reduce the angle 35 of attack. Likewise, anintentional or maneuvered decrease in angle of attack will shiftthecenter-of-pressure forwardly in relation to the center of gravity sothat this relative-change of location between the center of gravity andcen- 4 ter-of-pressure will tend to increase the angle of attack;thereby providinga self-stabilizing airfoil which will requiremaneuvered changes of angle of attack or superimposed, controlledchanges of angl'eof attack in order t'o ily it at an 4 'angle oi attackother than the'one at would normally tend to ily. Thus, a stable"airfoil will tend tojy at the same angle of'attack for any given airspeed if o it is so supported as to have the necessary freedom. l

Naturally, this function' of the type of airfoil which it lastdiscussed, namely, that function which is commonly recognized in theaeronauticield as the "stability of the airfoil,A is obtained onlywithin a practical range of angles of attack, and

' that range is sufiicient for practical operation.

This means, naturally, that if the angle. orattack on the airfoil wereputin reverse, that is, 60 if it were negative, the airfoil might or:night not have the stability hereinabovediscssed. Hence, th'e- .stableregion" of a stable airfoil, namely, one in which the center-of-pressuremi grates rearwardly with increases in angle yoi at- 65 tack has .been aterm well recognized and generally'accepted in theaei'onautic sciencesas the region bounded on'one side by the resultant airfloadvectorcorresponding to the minimum angle of attack at' whicn'jthebladeunretains this 7o.

stability function and bounded on the'other side by theresultantair-load vector corresponding to the maximum angle oifattackl at whichthe blade .still retains this stabilityv function.

Hence,.the. term, stable region. may be de-AJ 'I5 fined as the segmentor truncated segment swept by all the resultant air-load vectors whichshift rearwardly with increasing angles of attack and forwardly withdecreasing angles of attack.

The weighted average chord-section of anairfoil is that chord-section ofan airfoil blade which represents the average chord-section oi' all thechord-sections of the blade along ,its entire length; each weightedaccording to its aero-dynamic effectiveness.

For different forward speeds and engine lutions per minute, the mosteffective angles of incidence will be different, but a propellerdesigned so that it nds automatically the most advantageous' angle ofattack, say 5.4, at one Vspeed (preferably its cruising speed), will, in

general, maintain approximately the same angle of attack at otherspeeds. The turning moments about the axes AP being zero, the blades maybe said to Loat at the proximity of their most advantageous angle ofattack.-

However, the shifting relative position of the various forces acting onthe propeller blades under'changing conditions of speed and torquesometimes produces a flutter or hunting action about the axes AP and forthis reason I prefer to provide a means Ifor damping the motion of eachblade AB about its pitch-varying axis AP. For this purpose, I haveillustrated in Figures 1 and 6 a damping means comprising a cap 44attached to each blade-root bracket or arm 28 over the outer end of itscorresponding pivot 22. The cap 44 is half round at one side of thepivot 22 and elongated at the other side to form an oblong chamber 45which is filled with heavy oil. On the end of the pivot 22 is a radialfin 46 which extends into the' elongated section ofthe chamber 45, asmall clearance being left between the edge of the fin and the innerface of the cap at one side. The iin and pivot extend clear to the innerface of the iiat outer section of the ,cap so that when the cap isturned with respect to the fin by movement of the bearing 28, oil willbe forcedfrom one side of the iin to the other but at a restricted ratexed by the clearance between the n and the cap so as to produce adamping action. l Y

When the propeller or rotor is in operation, the centrifugal force willkeep the oil in the cap 44.

but to prevent loss from leakage along the bear-` ing between thebracket or arm 28, and thepivot 22, when the propeller is stationary, Ihave provided a packing 548 seated in a rabbet in the bracket or arm 28at the inner end. of the pivot 22.

I find it advantageous, moreover, incertain cases, tocombine with theautomatic means heretofore described for determining the angle of attackofthe blades 24 with an operator controlled means whereby such angle maybe set as desired. I have illustrated such a means in Figure 1comprising helical slots in the sleeve 34,

one of which appears at 48. In each of the slots 48 is a pin-52 carriedat the end of a bar 54, the other end of which is xed to a channelledring or collar 56. The bars 54 are mounted to slide in longitudinalslots 58 in the sleeve I8 (and the collar 56). Pins 52 may be movedaxially on the sleeve I8 by means of a lever 68, pivoted at 62 andhaving branched arms 64, 64, carrying pins 66 which project into thegroove or channel in the ring 56. By swinging the lever 60, and there-Afore. moving the pins 66, the pins 52 may bemoved longitudinally ofinner sleeve I8 to turn the sleeve 34 about the axisof rotation andthereby turn the blades 24 about their individual pivots revo-4 22 bymeans of gearing 80 and 82, so as to set the blades to have the desiredangle of attack. It will be understood that the operators seat is at therear of the engine indicated -in dotted lines at 68, and .a hand lever10 is provided for the operator which is connected to the lever 68 bymeans of a link 12., Therefore, when the operator moves the hand lever10 he adjusts the angle the complemental 'angles of the sides of thenotches 16 and the sides of the`lug 18, when there is pressure betweenthe contacting faces of the lug and any given groove, the lu'g is lockedin the groove but when such pressure is absent due to a. balance offorces on the blades, lug 18 may spring out of the notch`16 asillustrated in Figure '5. To produce such automatic release of the lug18 and notch 16, I prefer to'make .the lever 18 somewhat flexible andresilient in f the -direction transverse to the plane of the bar or.quadrant 14, so that the lug 18 will be resiliently tensioned in adirection away from the quadrant 14 which carries the notches 16. Whenaccelerating or-power-driving the propeller or rotor there is enoughpull on the connecting link 12 to retainthe lug 18 in engagement withthe inclined side of the notch 16. When, however, the power is cut offor the engine throttled down, or the power in any way disconnected,

' 14 has inwardly flaring notches 16 therein and then the spring 'snapsthe lug .18 outwardly into the position shown in Figure 5, so as torelease the'blades into their normal balanced pitch position. By, thismeans, there is an automatic release of the pitch from any of the lockedpositions. The operator controlled means for setting the bladesis usefulfor preventing automatic shift of the angle of attack during lstarting aplane from the ground, or in ilying'at y high altitudes withsupercharged engines, in making marked changes in the throttle setting,and under other conditions. A

The centrifugal Iforces on the direction of the plane perpendicular tothe axis' of rotation AC `cause friction at the bear-L ings between the'brackets or arms '28 andthe pivots 22, and may cause binding unlesssome means is used to prevent it. In'the arrangey ment illustrated inFigure 1, I show for this purpose a flexible cable III connecting theinner ends of the 'two blades 24. Such connection is obtained byspreading the ends of the cableas shown at in -re'cesses #82 in theendsvof the roots of the blades andthreading hollow nuts 84 into theinner ends of the blade roots 26 to force the sleeves 86 a inst thespread ends of the cable to hold thef nfplace and put it under initialtension. Whe fthe blades swing to some extent about the pivots 22, thedistance between the inner ends of the blades is decreased and thetension in the cable III would thereby be the bases 24 my relaxedlexceptthat the cap nut 85 at the outer are taken up by anti-frictionbearings. i

. are formed integral cured together `Yswivelled ring |06 and shafteither to vention illustrated' in when the blades` have moved out'of theline thereby maintaining the tension on the cable.V

embodiment of my invention in which the centrifugal forces in thedirection of the bladeaxes In. the arrangement shown in Figures 7 and 8,i6' is a driving shaft having a hub I8' thereon on which pivots 22,'.Blades having roots 26', 26', have the inner endsof their roots enlargedto form brackets or ar s 28'fmounted on the pivot 22' by means ofrolifler bearings 88. The blade roots 26 are secured, in the positionillustrated, relative to the hub I8' by a cage 90, formed in two partswhich divide along the line 92 passing through the center ottheshaftI6'. The two halves of the cage 90 are normally sef by means of bolts94, 94, and the two halves each have anges 96, 98, which pro- ;ie`ctover shoulders 98, 'on lthe brackets 28' so as to hold the blades intheir proper position. Anantifriction bearing |00 located between theflanges carrying the centrifugal loads reduces the friction resistingthe turning of theblades on their pivots 22.

Each bracket or arm 28' has in one face thereof arecess formed in partby a hood |02 in which is a ball |04 xed to a ring |06, on the shaft I6'at the end of a projection H0. The ring |06 is swivelled on the shaftI6', but held in place thereon against the sleeve I8' by the nut i08.The

ball IM serve to synchronize the movements of the blades 2B' on thepivots 22'. No operator controlledmeans has been illustrated in'Figures'I and 8 for adjustment of the angles of the blades'on pivotsl 22', butthe automatic adjustment by operation of aerodynamic forces andcentrifugal action occurs in the same manner -as-described in connectionJvith Figure 1.

-In Figures 9 to 14 further embodiments or extensions ofthe presentinvention-to illustrate its applicability to lift propellers ofrotative-winged craft, commonly called rotors, and toillustrate themanner in which the pitch setting of the blades canibe made responsive-to torque variations in the hub or increase the lpitch with theincrease of torque or to decrease the pitch with the increase of torque,depending merely upon a revxisersal of the angle of inclination of pivotto blade a Thus, in Figures 9 and 10 the spar or blade root 20,-44 ofthe-rotor blade 2l-a is connected to the rotor hub or rotor hubappendage or'v rotor hub extension: 2H througha pivot '2274i i clinedwith l'speetbto the blade-'abris AB by 62e angle f: the pivot 22 .-abeing so in relation to the hubaxis-AC and the blade axis AB that itsaxis. that is, the .pivot axis AP, will 'pass through the point ofintersection of hub axis and biadeaxis, jw. 1"he. structure.ofthevembodiment of the in- Figures 11and 12, as well as-that ofthe-embodiments illustrated in Figures 13 and-14. is similar to Figures9 and 10 in thatfall three embodiments are rotors intended lforproducingvertical lift.

In the arrangement f Figures 11 and 12, the v blade 24-1 is shown inFigure 11 in .its neutral position, the root ll-b of the blade 24-bbeingriveted uw an individual AB intersects the axis of rotation. In other orarms,

96 and the hub projections 98 for inclusive, there is illustrated um-mustrated 1n' ried -by the hub extension '20-b'. In Figures 11 and 12,the axis of rotation AC intersects the blade axis AB atv one point,whereas the axis o1' rotation AC intersects the axis of the pivot 22b ofthe individual blade at another point shown as lying above the neutralposition of the blade. In Figures 9 and 10, as well as in Figures 11 and12, the pivot axis AP inclines away from the. plane perpendicular to theaxis oi. rotation AC in the direction contrary to the direction of lift.

In the arrangement shown in Figures. 13 and 14, the blade 2l-c is shownin its neutral position in Figure 13, whereas the' blade root 26-c ispivoted -to an individual pivot 2.'ic whose axis is reversed as comparedto the pivots 22-b and 22-a. In Figure 13,l the hub extension 2li-c'carries the pivot 22-c in such a position that k.theaxis of such pivotintersects the axis 'of rotation AC below'tthe point at which the bladeaxis words, in Figures '13 and 14, the pivot axes AP incline away fromthe plane perpendicular to the axis of rotation in the same direction asthe directionof lift of the propeller type rotor.

. In Figures 11 and 12, the blade is shown for an increase in pitch withpositive torque, or decrease in pitch with negative torque while-'increase in pitch with positive torque and an increase in pitch withnegative torque. 'Ihe terml positive torque is here used to signify thetorque that would normally be produced with power imparted to the hub ordriving shaft, while negative torque is used to indicate the torqueproduced, for instance, by a braking action or a Figures 13 and 14, theblade is shown for a dedeceierating action on an already rotatingmember. The termsdecrease and increase" in relation to' pitch are usedwith reference to the predetermined pitch setting of the blade in itsvneutrai position.

In propeller rotors such as illustrated in Fig-v ures A9-to 14inclusive, when used for creating lift in Autogiro machines, therotation'being due to the reaction oi' the air on-the blades, thereislittle or no net drag in the plane'perpendicular to the main .axisoirotation and the positions of the blades on their pivots 22-a, 22-b,and 22-c and, therefore, their angles of attack' are determined almostentirely by the torque or inertia force and air force andthe centrifugalforce. I find that, Iby varying the relative position of -the pivot axeswith respectbto the mainv axis of rotation, I can increa'se; or decreasethe relative .ei- -fect of the centrifugal force onrthe blade The varrangement shown in Figures 9fand 10, is simi- `lar to that shown inFigure 1 where the centrifugal force acting on the blade 2|-a at a givenspeed of rotation and angle' of lag behind the neutral point issubstantially eliminated as compared to that acting in the formsillustrated in Figures 11 and 12 or 13 and 14.v 'Ihis is due to' thefact that in the arrangements shown in Figi ures 9 .and 1G the line fromthe-center o! inertia CI to the axis of rotation AC passes substantiallythrough the pivot axis in its neutral position.

-The restoring forcearesulting from thje centrifugal forces in this caseis substantially lZero. In

-the case of angular pivots :2-bf and 22-`c. thev perpendicular from CIto the laxis of rotation AC moves away from the axis AP ,as the blades24-b and 2li-c are denected lfrom neutral, so that the perpendicular nolonger intersects the axis AP.

This movement of the center of inertia CI in relation, to its neutralposition and the pivots 22 -,b and 22-c induces 'a restoring momentpivot is thereby generated equal to the centrifugal force multiplied bythe perpendicular distance between the center of the pivot 22-b orf- 22cand the line from CI to AC. In Figure 14,

the moment arm 'is indicated by the distance between the two arrows ZIM.

In each of the arrangements illustrated ln Figures 9 to 14 inclusive,there is a pivot 200 between the main axis of rotation of the propellerand the hub extension 20-a'20b' or l-c', respectively, such pivot 200lying in a Y plane substantially at right angles to the axis of rotationand being required when the propeller or rotor is used for creatingvertical liftin order to avoid the effect of unsymmetrical lift on thecraft.

In the formof my invention shown in Figures 9 to 14 inclusive where theflapping or coning hinge pivot 2" is incorporated, the blades cone upaboutv this pivot in night. Due to the fact that the blades are abovethe plane of the disc when coned up, there is a component of thecentrifugal force which is normal to the longitdinal blade axis andwhich acts to oppose the lift forces produced .by the air-loads (whichairloads manifest themselves visually inthe coning) This downwardnormalcomponent of the centrifugal force, opposes the lift forcescreating the coning, and maintain a balance therewith (along withinertia forces) about the. coning pivots. When the pitch-varying pivotsare inclined in any of the ways shown in this application, and moreparticularly in Figures 9 to 14 inclusive, then this normal componentofthe centrifugal force is not only effective about they coning pivotsbut is also effective about the pitchvarying pivots which likewisepermit the up .and

down displacement'of the blade (that is, more or less in a directionparallel to the rotor hub axis). In the embodiment shown in Figures 9 to1 2 inclusive, where the axis line of the pitch-varying pivot projectsbelow the blade, this normal component of the centrifugal force has an.unstable influence, so that whenever the blade is not in what may beregarded as a center position with respect toA said pitch-varying pivoton one hand vand the said'normal centrifugal component on the otherhand, said normal centrifugal component will tend to' accentuate themovement about said pitch-varying pivot. Howevenin the embodiment of theinvention shown in Figures 13 and 14 where the axis line of thepitch-varying pivot projects above the blade, the downward normalcomponent; of centrifugal force has a stable' inuence with respect tothe pitch-varying movement and tends to centralize the blade withrespect to the pitch-varying pivot.

1n the former case (Figures 9 to 12 inclusive), i

the stability of the blade is dependent on the 'aerodynamic forces andthe component of the centrifugal forces which is parallel to the bladeand which thereforeV tends to center the blade about the pitch-varyingpivot in the forms shown in Figures 11 and 12 (and also in Figures 13and 14). In the embodiment-f the invention shown in Figyes and 14, notonly does the centrifugal force component parallel to the blade tend tocenter said blade about the pitch-varying pivot but also the centrifugalcomponent normal to the blade also tends to center the blade about saidpitch-varying pivot. Thus, in the form of my invention shown in-Figures13 and 14, the normal component of the centrifugal force will have aself-centering or stabilizing influence, but inthe 5 forms" shown inFigures 9 to 12 inclusive, the normal component of the centrifugal forcewill have duced .by the air force and any `self-centering eifect of thelongitudinal component vo f the centrifugal forces which may be presentmust be suiciently effective to overcome the4 unstable moments of thenormal component of the centrifugal forces (which normal component actsto oppose the lift forces) for any given operating conditions.

While I have shown the axes of the pivots for the individual |blades inall cases as lying in` planes radial tothe main axis of rotation of thepropeller or rotor and intersecting the main axis of rotation but at anangle other than a right angle and the blade axes as always intersectingtheir individual axes, I do not limit myself to either condition.Neither do I limit myself to always setting the blade axes so as tointersect the main axis of rotation.

Having thus described my invention,.what I hereby claim as new anddesire to secure by Letters Patent is: I

1. In an aircraft, a revoluble thrust-producin system including a hub, agenerally radially disposed airfoll blade pivotally secured to andcarried by said hub by a vcorresponding single pitchvarying blade-rootpivot Whose axial line of pivotation is fixed in relationl to thelongitudinal axis of the blade-root and passes outwardly from said hubon the back or-pressure side of the airfoil blade in a generally radialdirection and diverges from the arfoil blade as it goes outwardly fromsaid hub, nd, passes through tl'e stable region of the resultantair-load vectors of the airfoil.

- 2. In an aircraft, a revoluble thrust-producing system including ahub, a generally radially disposed airfoil blade'pivotally secured toand carried by said hub by a corresponding single pitchvaryingblade-root pivot Whose axial line of pivotation is iixed in relation tothe longitudinal axis ly outward on the back or pressure side of theairfoil blade andis so disposed in relation to the i weighted averagechord-section of the airfoil as v that at which.they tend .to maintainthemselves at steady rotation .by virtue of the aforesaid Apivotationand for releasing said blades at will to permit them to assume their'normal angle ofattack. `3. In an aircraft, a revoluble thrust-producingsystem including a hub, 'a generally radially disposed airfoil bladepivotally secured to and carried by said hub by a corresponding` singlepitchvvarying blade-ootpivot whose axial line of pivotation directedgenerally radially outward on the back or pressure side of the airfoilblade and is so disposed in,relation to the weighted averagechord-section of the airfoil as t0 cause the air- 75 In the of theblade-root and is directed generally radialy termined angle of attack(about said pitch-vary- -ing pivot) when revolving at a constant speedand without acceleration or deceleration, manually loperable means forretaining the blades at a reduced angle of attack, namely, at an angleof attack below that at which they tend to maintain themselves at steadyrotation by virtueof the aforesaid pivotation, and automatic Vmeans forreleasingsaid blades to permit them to assume ltheir normal angle oi'attack upon attaining a predetermined speed.

4. In an aircraft, a revolublethrust-producing system .including a hub,generally. radially disposed airi'oil blade pivotally secured to andcar.- ried by said hub 'by a corresponding single pitchvaryingblade-root pivot carried'by a blade-flap ping pivot, the axial line ofpivotation of said pitch-varying blade-root pivot being fixed vinrelation to the longitudinal axis of the blade-root and passingoutwardly from said hub on .the back or pressure side of the airfoilblade in a generally -radial direction and diverging from the airfoil.

blade as it goes outwardly from said hub, whereby said airfoil bladewill tend to oat ormaintain l operable means for retaining the blades ata reitself at a predetermined angle of-attack (aboutl said pitch-varying.blade-root pivot) when revol'ving at a constant speed andwhereby saidangle of attack will be increased byy increase i`n driving torque anddecreased with decrease in driving 5. In an aircraft, a revolublethrust-producing system including a hub, agenerally radially disposedairfoil blade pivotally secured to and carried by said hub by atrunnion-like pitch-varying blade root pivot whose axial line ofpivotation is fixed in -relatioz'i to the longitudinal axis of theblade-root and passes. outwardlyfrom. said hub on the back or pressureside ofsthe airfoii blade in a generally radial direction and divergesfrom thejairfoil blade as it goes outwardly from'said hub, andpassesthrough the stable region'of the resultant air-load vectors oftheairi'oil.

8. In an aircrafha revoluble thrust-producing system including a hub, agenerally radially disposed -airtoil blade pivotally secured to andcarried by said hub-by a t1'unnion'like` pitch-varying blade root pivotwhose axial line of pivotation isv in relation to' the longitudinal axisQ1' the blade-root and is directed generally radially outward on theback or pressureside of the airi'oil blade and is so, disposed i'nrelation to the weighted average chord-section o! thejairfoil as aasniacl to cause the airfoil blade tend to oat or maintain itself at a,predetermined: angle of attack,

about said pitch-varying'blade-root pivot, when revolving at a constantspeed and with acceleration or deceleration, and manually operable meansfor retaining the blades, at a reduced angle of attack, namely, at anangle of attack belowJ that at which they tend to maintain themselvesatrsteady rotation by virtue of the aforesaid pivotation and forreleasing said. bladesat ywill `to permit them to assume their normalangle of attack.

7. In an aircraft, a revoluble thrust-producing system including a hub',a generally radially disposed airfoil blade pivotally secured to andcarried by said hub lby, a trunnion-like pitch-varying blade root pivotwhose axial line of pivotation is directed generally radially outward onthe back or pressure side of the airfoil bladeand is so disposed inrelation to the weighted average chordsection of the airfoil as towithout acceleration or deceleration, manually duced angle of attack,namely, at an, angle of attack-below that at which they tend to maintainthemselves at steady rotationy by virtue of the aforesaid pivotation,and automatic :means for releasing said blades to permit themto assumetheir normal angle of attack upon attaining a 'outwardly' from s aidihubon the back or pressure side of the airfoil blade in a generally radialdirection and diverging from'the airfoil blade as it goes outwardly fromsaid h ub, whereby said airfoil blade will tend to'iloat'or `maintainitself at a predetermined angle o f attack, .about said "pitch-varyingblade-root pivot, when revolving at lla constant speed and whereby saidangle 'of 'attack will be 'increased by increase in driving torque anddecreased with decrease in driving torque'.

' RICHARD H. PREWI'r'r.l

danse the airfoil to tend to float or maintain itself at a predetermined angle of attack, about said vpitch-varying a pivot, when revolvingat a constant speed and DISCLAIMER 2,234,196f-4Rz'chard H. Prewtt,Lansdowne, Pa. PROPELLER 0R Ro'ioR CONSTRUC- TIoN. Patent dated Mar. 11,1941. Disclaimer filed May 22, 1945, by the patentes. Hereby enters thisdisclaimer to claims 4 and 8 of said patent.

lOjcial Gazette July 10, 1.945.]

